Revisiting the Reaction of Sulfur Ylides with Acetylenic Esters: Synthesis of Trisubstituted 1,3‐Dienes, α‐Carbonyl Vinyl Sulfoxides and α‐Carbonyl Vinyl Sulfoxonium Ylides

We report herein a reexamination of the reactions between sulfoxonium ylides and acetylenic esters. Continuing our previous study of conjugate additions using α‐carbonyl sulfoxonium ylides, we came across an interesting transformation when dimethyl acetylenedicarboxylate (DMAD) was employed as a Michael acceptor. Trisubstituted electron‐deficient 1,3‐dienes and α‐carbonyl vinyl sulfoxides were obtained for the first time from these sulfur ylides, in a stereoselective manner (exclusively forming the E‐isomer), achieving yields of up to 70 % and 83 %, respectively. Selected dienes were subsequently utilized in the synthesis of novel nitrogen heterocycles. Interestingly, when di‐tert‐butyl acetylenedicarboxylate (DtBAD) or alkyl propiolates were evaluated, the isolated product arose from the classical Michael addition, yielding α‐carbonyl vinyl sulfoxonium ylides in yields of up to 89 %. A new method to access (E)‐1,3‐dienes, (E)‐vinyl sulfoxides and vinyl sulfoxonium ylides (VSY) in a single step from α‐carbonyl sulfoxonium ylides and acetylenic esters is described. Selected examples of 1,3‐dienes were subsequently utilized in transformations involving intramolecular cyclizations, providing new nitrogen heterocycles.